The present invention relates in general to sewing machines and in particular to a new and useful sewing arrangement and device for moving a workpiece to accurately move it through positions for sewing seams thereon.
A similar feed device is known for example from U.S. Pat. No. 4,419,946, dated Dec. 13, 1983 and comprises two links, each provided with a drive, which are articulated to two pitmans and forms with them a parallelogram. At a section of one of the pitmans extending beyond the parallelogram, a work holder pivots about a hinge pin. The hinge pin is connected via toothed or gear belts with an additional drive, in order that the work holder can be pivoted about the hinge pin. The toothed belts, which are disposed in the interior of a link with rectangular hollow section and in a pitman of the same design, are passed over gears and over a pinion connected with the additional drive. During sewing, the parallelogram is pivoted about a fixed bearing, at which the two links engage. Thereby the gears supported in one of the links or one of the pitmans are oscillated about the pinion, which is fastened on a shaft of the additional drive disposed in the fixed bearing. With this drive standing still, the gears are rotated relative to the stopped pinion in the course of the pivoting movement of the parallelogram just far enough for the work holder to be displaced parallel to itself, i.e. in a purely translatory movement.
Because toothed belts are used for the guiding of the work holder, faults may occur due to elongation of the belts, which at high sewing speed are under heavy stress. The amount of these elongations depends on the load as well as on the state of the belts. In case of frequently occurring, relatively strong elongations the belts are moreover subject to considerable wear, so that they may have to be changed often.